The invention relates to a method of analog signal processing of video signals from picture elements arranged in an array, which are adapted for discrete scanning in terms of time, using a resistive network. Moreover, a device in this respect is described.
In analog image processing resistive networks, which are often also referred to as electronic retina, are used for filtering the video data. These devices serve the purpose, inter alia, of intensified representation of edges in the video data by a vertically exaggerated transition in contrast; continuous signal variations with a lower local frequency (as they are caused, for instance, by drifting signals) should be suppressed and represented by a signal of medium intensity.
Compared against filter operations performed on digital computers the analog video processing technique offers the advantage that the video data is processed in parallel so that a higher processing rate can be achieved at a reasonable expenditure in terms of hardware.
When the picture elements of video sensors are processed which have a flat configuration and are composed of individual picture elements arranged in an array, each picture element must be imaged onto a node of the resistive network, i.e. the electronic retina, where a circuitry is provided for signal transmission and forwarding. The video information of each picture element is three-dimensionally filtered by forming the difference between the potential distribution occurring on the resistive network, on the one hand, and the actual halftone picture achieved.
Such an integrated solution of the video sensor and the electronic retina is described by M. A. Sivilotti, M. A. Mahowald, and C. A. Mead in: xe2x80x9cReal-Time Visual Computations Using Analog CMOS Processing Arraysxe2x80x9d, Stanford Conference VLSI, Cambridge, MIT Pres., pp. 295-312, 1987, as well as by H. Kobayashi and J. L. White, and A. A. Abidi in: xe2x80x9cAn Analog CMOS Network for Gaussian Convolution with Embedded Image Sensingxe2x80x9d, IEEE International Solid-State Circuits Conference, pp. 216-217, 1990. The known solutions, however, present a distinctly reduced three-dimensional resolution and a lower filling factor as a result of the increased number of devices which are required per picture element. In combination with the small image field size which can be realised optical effects such as aliasing produce an interfering effect.
The achievable image field size is, however, also restricted in the case of a separate retina device (without a separate sensor) for pre-processing video data which is recorded with an independent camera. Even when such a device is manufactured in a highly integrated process only sectional images can be processed with the chip sizes available, which sectional images represent only an insufficient patch from the total image.
System arrangements with parallel application of several retina devices are fundamentally realisable but the advantage which the analog processing promises in terms of system costs, processing time and stray power in comparison against digital image processing systems, is minimised by such a set-up.
The invention is now based on the problem of providing a method of analog signal processing of video signals from picture elements arranged in an array, which are adapted for discrete scanning in terms of time, using a resistive network, in a form permitting the processing of signals from two-dimensional sensor arrays having a distinctly wider area than the processing network as such. In particular, the invention aims at an improvement of the demands in terms of efficiency and area, as they prevail, for instance, in current image pick-up devices.
The solution to the problem supporting t he present invention is the subject matter of claim 1. An inventive device for carrying through the inventive method according to claim 1 as the subject matter of claim 7. Features relating to an expedient improvement of the inventive idea are the subject matters of the dependent claims.
The invention starts out from the idea to operate the array of the electronic retina in a xe2x80x9croll-overxe2x80x9d mode. The video sensor having a flat configuration is quasi xe2x80x9crolled overxe2x80x9d by an electronic retina which has preferably the shape of a cylindrical structure, wherein a video signal is transmitted from the picture elements arranged in the video sensor array to the individual network nodes of the electronic retina. The figurative comparison with a retina rolled up to form a cylinder serves for a better understanding of the signal transmission which takes place by means of an appropriate addressing of the picture elements and node points on the retina for signal transmission.
In accordance with the present invention the method of analog signal processing of video signals from picture elements arranged in an array, which are adapted for discrete scanning in terms of time, using a resistive network, the so-called electronic retina, having a two-dimensional field structure including a number of lines m smaller than the number of lines p of the picture element array, wherein the video signals are transmitted from the picture elements in the electronic retina by lines, is characterised by the features that, starting with the first line of picture elements, the video signals are transmitted into the first line of the electronic retina until after the transmission of the video signals from the m-th line of the picture element arrays into the m-th line of the electronic retina the picture elements of the m+1st line of the picture element array are transmitted into the electronic retina, starting again with the first line, until the p-th line of the picture element array is transmitted in a roll-over manner into the electronic retina, and that between every two successive operations of roll-over transmission of video signals to the electronic retina the respective retina lines are read out via an independent signal line without any influence on the transmission operation.
The inventive use of the electronic retina offers a problem solution by a multiple use of the resistive network which could also be referred to as time multiplexing or roll-over operation.
With the electronic retina not comprising a sensor part there is no invariable allocation between the circuit elements of the resistive network and the geometric picture elements of the video sensor having an array configuration so that an optional assignment of individual network areas of the electronic retina may be made for image processing.
The resistive network, which is constituted by retina elements, typically presents a network characteristic with a restricted remote effect which behaves like an equivalent of the Gaussian function employed in digital filter operations. The coherence lengths usually employed in image processing are substantially smaller than 5. This means that only a limited number of adjacent picture elements takes an influence on the output value of a picture element. Potential influences over a distance exceeding three coherence lengths (K) disappear in noise.
For a transmission of the sensor signals by lines this means that after the read-out of the retina image data from line n into line n-k with k=ck new video data may be written. The new video information need not be expected to take an influence on the retina output if the constant c is selected to be higher than 3.
The decisive advantage of the invention resides in the aspect that a retina with a limited number of lines can be used for real-time processing of video information of a camera chip with a large number of lines.